Observations on the Courtship and Reproduction of the Desert Pupfish (Cyprinodon macularis)

By Tom Baugh
reprinted from American Currents, Spring 1981

Specimens of Cyprinodon macularis were collected from the Salton Sea area of
Southern California on April 23, 1979. All specimens were fed commercially prepared frozen
brine shrimp. The water from which the fish were taken was highly saline. The fish were
transported by air from California to Utah where they were placed in a 20-gal aquarium
with saline water. During the next two weeks the salinity of the water was decreased by
drawing off the water in the aquarium and replacing it, through drip application, with
fresh water. At the end of two weeks desalinization was complete and fish had adjusted to
the change. With the exception of one mature male, all specimens were immature.

By the first part of July several females had attained a length of about one inch. Two
of the females were placed in a separate 20-gallon aquarium with the one mature male. One
of the females was apparently gravid.

On July 9, 1979 I made a partial water change (2 gal) in the 20 gallon aquarium
containing the mature fish. The following day I noticed that the male was sporting
courtship colors. The upper portion of his back was a metallic powder-blue. The dorsal fin
was black, the posterior edge of the anal fin was edged with black and the caudal and
pectoral fins were colored a light lemon-yellow. The male divided his time between
nuzzling the gravid female and chasing both females.

About 24 hours later the courtship pattern had changed. The gravid female was suspended
about four inches from the gravel substrate. The male, resplendent in his courtship
colors, tightly circled below the female in a clockwise direction. He would pause, resting
close to the bottom and then return to the female, circling counter-clockwise. During this
time the female hung motionless in the water. On occasion, the female would drop to the
bottom where the male would nuzzle her. Also on occasion, the female would dart away
pursued by the male.

Three days (July 22) following the onset of courtship I noticed the previously swollen
abdominal region of the female was flat. Apparently spawning had occurred during the
evening or morning hours. I removed the artificial spawning grass and noticed about ten
small eggs (ca. 1/32 inch) attached to the thin plastic strips of the spawning grass.

I removed the grass from the aquarium and placed it in a one-gallon container which
contained the same water as that from which the eggs were taken. An airstone was used to
mildly agitate the water. The water temperature averaged 74F from the time of spawning
until the first free swimming larvae was noted on July 20, 1979. The pH was 7.4.

Shortly after hatching, the larvae appeared to be about 3/16 inch in overall length. It
took from 2-3 days for the yolk to be absorbed. Within the first several days following
hatching the larvae lay in the small amount of detritus along the bottom of the container.
By the fourth day following hatching, several of the larger larvae (ca. 1/4 inch) were
noted darting about the container apparently capturing brine shrimp nauplii. Twelve days
following spawning all of the original eggs had hatched.